GMAT PREP Arithmetic Mean???

dferm, the question that you have posted are some of the basic kind of questions. I suggest that you go through the math basics again in order to brush up your basics. Kaplan Math workbook or the five different books from Manhattan will certainly help

Basically this question you need to understand the impact of single element on the average. If there is one director, he increases the average by 15000. To bring the average back to original value, you need to add more managers. Each additional manager will decrease the average by 5000, so three managers will be required to bring the average back to normal. And this trend will continue. So for every director you will need three managers...
Hence the ratio is 1:3

I am having problems understanding these types of questions for some reason...I am doing well overall on the OG11 and Math Review but when I am doing the GMAT PREP some of the questions are mind boggling..I have reviewed all the MGMAT books but still am not getting a grasp on the logic here...What do you suggest? Can you please help me?? I have the test in two weeks but I seem a little lost with the GMAT PREP....

SimplyJat.....

Please answer the question..what is the answer...your explanations to these questions are not helping me..you are just putting me down...and that is a no no...I need encouragement...it takes some of us a little more time....

I wanted to point you to the way of thinking. In this question you need to understand the basic concept of counting and statistics.

Lets analyze a list. 15, 5, 5, 15

Take the first number. 15
The average is 15 / 1 = 15

Take the second number 5 (notice that this number is less than the current average.)
The new average is ( 15 + 5 ) / 2 = 10 ( and thus the average reduced )

Take the third number 5
The new average is ( 20 + 5 ) / 3 = 8.33

Take the third number 15
The new average is ( 25 + 15 ) / 4 = 10

So seeing all these we know that if the new number added to the list is higher than the current average it increases the average and vice versa.

So coming to you question of managers and directors. you need to know the ratio of managers to directors. Or how many managers for each director. Statement I tells that the average salary of director is 15000 more than the average and statement II tells that average salary of manager is 5000 less than average. Individually these statements are insufficient as they talk only about one aspect; either manager or director. But combined together we know the relative average salaries of manager and directors and using this information we can find out what is the ratio of manager to directors.

Lets assume that current average is zero. salary of director is +1500 and salary of manager is -5000.
So you start adding managers and directors till you reach the average of zero again.

Add a director... new average is 15000 / 1 = 15000
Add a manager... new average is 15000 - 5000 / 2 = 5000
Add a manager... new average is 10000 - 5000 / 3 = 1667
Add a manager... new average is 5000 - 5000 / 4 = 0... whoa we got back to the initial average of zero. by adding one director and three managers. So, there are three managers for every director in the company...

Hope it clears the doubt

Now we are on the same page in terms of helping each other out...


Thanks.

This cleared this question out of my head...

Now the question is...Do you suggest that I start practicing from GMAT prep exclusively and anything I don't understand to review....

Please advise..


Thanks...

Near the end of your studying, I recommend understanding all GMAT Prep Quant questions you come across. More often than not, you can google the answers, but you're free to post here; we're all here to help.